First bits of extracting image overlay control to won class, to prevent the use of videotestsrc (slow) alpha's
* Adapt to form to new imageoverlay.
* Move Gst.Element tweak's control to ImageOverlay class
* Clean rests of adaption to form to new imageoverlay.
* Adapt settings for new image overlay
Merge pull request #2 from aleixq/imageOverlay

Image overlay own implementation